The present invention relates to a wear-resistant coating on sealing strips of rotary engines having a trochoidal chamber and more particularly to a wear-resistant coating for a trochoidal chamber made of a supereutectic aluminum-silicon alloy, to the sealing strips containing this coating, and to the method of producing such a sealing strip.
For the proper operation of rotary engines, it is important to provide a particularly good dissipation of the combustion heat as well as movement without wear of the partners which seal the combustion chambers. The friction partners which seal the combustion chamber are the chamber walls of the rotary engine which have a trochoidal shape and sealing strips disposed at the corners of the piston. Materials with good heat conductivity are best suited to dissipate the combustion heat and have been used for the trochoidal chamber walls. In the past, light metal alloys preferably have been used for the trochoidal chamber walls. These materials, however, generally have such low stability and wear-resistance that the trochoidal walls must be provided with reinforcing coatings. Thus, coating sold under the name ELNISIL have been found acceptable on light metal trochoidal chamber walls. Those coatings consist of electrodeposited nickel layers with inserted SiC particles and are produced by NSU-Motorenwerke/Germany. Their friction partners, the sealing strips, may be made of a hard metal or ceramic sinter materials.
Recently, the development of supereutectic aluminum-silicon alloys resulted in a light metal which, due to its good heat conductivity and its simultaneously improved hardness and wear-resistance, can be used for producing trochoidal chambers so that their contact surfaces no longer need be protected by a special coating. For instance, such supereutectic aluminum-silicon alloys are described in U.S. Pat. No. 3,333,579 and consist of 16 to 18% silicon, 4 to 5% copper and aluminum in balance.
Conventional sealing strips, mainly those made of hard metals and ceramic sinter materials, are too aggressive compared to the trochoidal chambers made of supereutectic aluminum-silicon alloys and these sealing strips cut into the trochoidal contact surfaces and destroy them.
Piston engines with cylinders made of supereutectic aluminum-silicon alloys are known to produce good results when the sealing elements, that is, the piston rings, are provided with an electrolytically deposited hard chromium layer. Tests on rotary engines with chromium-plated sealing strips, however, were unsuccessful. The reason for this is mainly that the electrolytically deposited layers are too thin for the amount of wear involved, while thicker electrolytically deposited layers could easily clip off or break as a result of developing internal stresses. In addition, the lubrication conditions in a rotary engine are less favorable than in a piston engine so that the sealing strips with electrolytically deposited hard chromium layers easily lead to burn traces and binding pistons. Further, the coatings on sealing strips used in rotary engines are subjected to centrifugal forces so that better adhesion is required for such coatings than with coatings for piston rings.